As is known, geotechnics, building and the like typically use impermeable layers or elements which have the function of covering other materials or being covered by them.
Usually, the impermeable elements are provided by membranes made of medium- or high-density polyethylene, which are covered by, or cover, materials such as soil, waste, sludge, natural elements, concrete and so forth.
In the field of building, membranes are used both vertically and horizontally which are designed to isolate or separate the building from the ground, so as to create an isolation and drainage element.
In the geotechnical field, the membranes are used in the construction of landfills, both as waste containment elements that render the basin impermeable, and as elements for covering and sealing the landfill once it has been saturated.
In the first application, the membrane is covered and protected by additional spacers, which have the purpose of preventing perforations or damage caused by the covering material and allow to drain the sludge that is present on the bottom and also to block any leaks.
The spacers with draining and protective function are usually geocomposites, i.e., products constituted by the joining of plastic net and fabrics.
In the second application, the membrane, which is arranged to cover saturated landfills, is covered by additional spacers and then by soil, so as to drain rainwater at the upper face and fermentation gases at the lower face.
The spacers with protective draining function are typically geocomposites, i.e., products constituted by the joining of plastic nets and fabrics, or natural elements such as gravel or sand.
In all the cases cited above, the first purpose is to prevent the covering or covered materials from coming into contact with the membrane that must be protected, while the second purpose is to drain liquids and gases between the membrane and the covering or covered material.
With the solutions currently used, it is therefore necessary to use several separate elements, which are coupled one another at installation time, creating a multilayer element which substantially has at the center a smooth or corrugated membrane, which constitutes the impermeable separation element, while on the upper face there is a protective draining layer constituted by a geocomposite or by natural elements and, at the lower layer, by an additional protective draining layer, also provided by a geocomposite or by natural elements.
The use of mutually separate elements generates several problems of interaction and corresponding friction when the layers are applied to an inclined plane, due to the possibility of slippage of the covering material on the geocomposite and/or of the geocomposite on the membrane and/or of the membrane on the underlying geocomposite and/or of the geocomposite on the covered material.
To avoid the risk of severe collapses and damage, in current solutions the basin of the landfill or its covering must be provided with limited slopes.
Currently, the most widely used membranes are those that are smooth or slightly corrugated in order to increase their degree of friction with the covering materials.
Membranes are also commercially available which have protrusions on one or both faces, but these membranes too must be subsequently covered or cover layers of geocomposites or fabrics or natural elements in order to achieve the combination that is capable of protecting the membrane and of draining liquids and gases.
In particular, U.S. Pat. No. 5,258,217 provides a membrane that has conical or cylindrical elements both on the lower surface and on the upper surface, but additional layers are superimposed without binding on such protruding elements at installation time, so as to be able to provide both the protection function and the drainage function.
Another problem further consists in that the protrusions are very sparse and often have such dimensions that they do not constitute spacers adapted to protect the membrane.
Accordingly, the installation of such a membrane, with the need to apply the geocomposites subsequently, entails high costs, and the problems of interfacing between the membrane and the elements that are moved close to it remain unsolved.
The solution does not allow to provide draining systems, but facilitates grip between the sheath and the superimposed elements.
Other known solutions provide membranes that are preformed during the extrusion step, so that the membrane no longer appears flat but has studs shaped like a half-cone, which are matched by hollows on the other face; however, such preformed membranes, used predominantly in the building industry, have very low thicknesses and accordingly are fragile and must be coupled to fabrics in order to provide a draining system, which most of the times is ineffective due to the compressibility of the structure itself, so that the draining effect is limited exclusively to the side where the studs are convex, whereas on the other side the fabric adheres to the concavity, with consequent stagnation of liquids.
The spacing between the studs is such that the draining capacity is very limited and decreases significantly as the load increases.
These solutions, which do not allow to drain both liquids and gases, have no grip capacity and friction between the membrane and the covered material is absent.
There are also membranes provided with protruding elements on one face, such as for example the ones shown in U.S. Pat. No. 5,891,549 and U.S. Pat. No. 6,972,269, but these products allow to provide a draining spacer system only at one face, and therefore it is necessary to use them in combination with other draining elements on the other face and install them separately.
The face that has no protrusions has no grip characteristics and makes the membrane potentially slippery on the covered material, and accordingly does not solve the problem of the interface between the membrane and the geocomposite that is applied to one of the two sides.